I filled up may gas tank and drove home....when I got home I noticed a gas stain on my garage floor about a foot in diameter under the rear/passenger side (by the muffler). Two questions: 1) When I look down the filler neck, the gas it right to the top...could I have "overfilled" the tank? 2) I had just purchased a new locking gas cap, and even thought it appear to fit, I really never felt it fit the neck "like the old locking gas cap did". Could this be the culprit for the leak...not quite fitting gas cap? I swapped caps...so we will see.

 

The fuel lines come off the top of the tank on the passenger side and down to the frame rail. You should be able to see them from underneath with a flashlight. Mine were cracking from age and started to leak too. I just replaced them, problem fixed.
Greg

 

But why would it only happen when I filled up?

 

I don't know. It was just a thought as mine were bad. Maybe it is slightly overfilled.

 

But it has never done it before....The ONLY change has been the new gas cap. Can an ill-fitting cap cause a drain or spill?

 

Probably. Try re-filling it to the very top again and use you old cap. See if the problem goes away.

 

It sounds like it is related to what you had just recently done, changed the gas cap. I would replace it with the Stant brand of locking caps.
Good Luck
Steve

 

On my 69, there is a drain hose connected to the rubber boot around the fuel fill neck. If you have a real full tank, and it gets hot and expands, would the gas leak past the cap and drain to the floor? I assume that a 75 has a non-vented cap that shouldn't leak, if it is working correctly.

 

75's have non-vented caps. The spill tube goes behind the tank to the passenger side. Since the fuel pump pulls fuel from the tank, and also returns fuel to the tank, it's pressurized.. Could be blowing past the new cap and into the runoff tube.

 

I think you guys are right.....changed back to the original cap the same day I noticed the gas stain on the floor (Saturday) Drove it yesterday morning and sloshed the gas around (hard starts, hard stops, hard cornering) and had no leaks, no drips, no errors!!!! So it was the new gas cap. Seems like my Vette is VERRY VERRY pickey whenever I change anything on her....she lets me know whether she likes it or not....apparently she did not like the cap....BUT she like the new Borlas I installed Friday......

Thanks guys for all your input!!!

 

If your 75 tank is like my 72, there is a fuel vapor separator unit on the driver's side of the tank. It is mid-tank all the way at the top. There is a hose from the fuel system where fuel vapors are routed and then a fuel vapor is separated from fuel. Most of these plastic units begin to leak. Unfortunately, the plastic is a VERY stable type of plastic that has no known solvent that will allow it to be resealed. That last statement is not mine, but from an engineer at a solvent/glue manufacturing company that I talked with. The good news is that these fuel condensors have finally been reproed.

Here is a good test. With your car cold and on a level surface, fill your tank to the limit using a portable gas can. Watch the left muffler to see if any fuel seeps or drips onto it. That is the reason to do it cold. The engineers somehow designed this unit so that if it leaks, it leaks onto the hot muffler. Can you spell "BOOM"? If this is your issue, the unit is a major PITA to remove because you have to remove the two mounting screws by feel. 5/16" IIRC and then you have to replace it.
Your situation is identical to what I had and the culprit was the fuel condensor.

Here is a link to Zip Products. They say 70-74 but it doesn't hurt to check!

http://www.zip-products.com/Zip/sear...7D&position=48

Gary

 

vetteguy...

You are no doubt right, however... considering the age of your car and the fact that the gas seemed to be leaking on the passenger side, near the muffler, you really owe it to yourself and the car to perform a thorough inspection under there.

The overflow hose from the scupper drain around the fill neck is supposed to be routed to just behind the rear tag, in the center. It theoretically should not be dripping on the passenger side muffler. The feed line and the return lines to & from the fuel pump are however in the vicinity of the passenger side muffler.

If you can get the rear of the car in the air a bit you can slide under it on a creeper, if not a large piece of clean cardboard makes a handy creeper as well. Use a strong flashlight to take a good long look up around the gas tank. (Removing the spare tire carrier will make this job a whole lot easier, but isn't necessary unless you do find evidence of additional leaking.)

Any fuel leak will most surely leave a trail in the dust and dirt that accumulates around the gas tank and you're looking for something that appears recent. On the passenger side you should see where the hard lines from the pump interface with the tank using rubber fuel line hose. In the center rear, you should see the drain hose that comes from the fuel "scupper" around the fill neck. On the driver's side you should see where the tank interfaces with the hard lines that go to the front (charcoal canister), once again using rubber fuel line which tend to drip onto the driver-side muffler when they leak.

If any of these rubber lines are original, as some most likely are, they are probably due for changing. They're mostly short lengths of hose and not terribly difficult to replace. Definitely much easier to replace in your garage with all of your tools available, than some rainy night... 20 miles from home in a gas station parking lot, with marginal light.

Since it is a '75 you should also look closely at the tank in the vicinity of the retaining straps that hold it in the car. Many times the insulators that keep the straps from touching the tank deteriorate over time and will result in leaks where they either contact the tank or allow rust to develop. I replaced a tank on a '73 more than 10 years ago that was leaking (coincidentally on the pass side muffler). The straps and insulators were in fact hiding major holes from rust in the tank, that merely dripped... until I began to remove the tank!

The fuel system on these cars is really pretty simple and quite reliable. Most of it can be R&R'd by a halfway competent wrench, so don't be afraid of it. I'm sure you'll come away from a thorough inspection reassured that everything is well, but the peace of mind makes it a task well worth undertaking.

Good luck... GUSTO

 

I am having problems with my fuel system.. I have been smelling gas fumes for awhile now in the garage where my 71 Stingray is kept..
I am pulling the tank to clean it... But I looked underneath yesterday and I found the same situation you found . Stains on the drivers side muffler..
I am probably lucky I didnt take a moon shot. I pulled the spare tire and drained the tank this AM. There is evidence of leakage everywhere..
I have a stinkin feelin I am not going to like what I find when it is removed.. A look inside and the sock Lars referred to looks like a big rust ball along with more rust on the bottom of the tank..
I think the forum senior members should somehow pass this along because IT IT IS a dangerous Situation
Any suggestions on how and what to use ti clean the tank..???
Ron
Kingman AZ

 

Thanks GUSTO14 for the advice....

I will give it a complete inspection this weekend! You're right....the last thing I want to do is end up in the middle of nowhere with problems.....

 

the lid of the fuel vapor seperator is glued on, 30+ years ago.the glue lets go and causes the leak your describing, before they became available again, i was taking old ones and regluing the tops on and painting. i have 2 of these.1 on the car and a spare, havent had that problem since i glued it..here's one i already glued and painted-------------------------------------------------------------------------------------------

 

I checked with the shop manual (mine is a 75) and there is no fuel/vapor separator. They quit using they "thingy" in 1974....